Why is residential wiring known as single phase?

[rbalex]

Well, what is the phase for

sin(wt + 179)??

You answered that yourself back in 1566: (wt + 179)

 

[rattus]

Phase:

Phase:

You answered that yourself back in 1566: (wt + 179)

But then, phase for sin(wt + 180) is (wt)???

How can the phase suddenly change from (wt + 179) to (wt) ???

That is, how can you make the phase constant go to zero in an instant???

I guess it is just over my thick head. Sounds like a discontinuity to me!

 

[Besoeker]

I have already accepted the wave forms are not "in phase", but I assert there is a difference between "in phase" and "same phase" since every relevant system voltage function can be validly written in terms of a common identical phase; i.e., the "same phase."

I think that's where we differ.
The two waveforms can be expressed with reference to a common phase.
That they can doesn't make them the same phase.
They have a mutual phase displacement of 180deg.

 

[rbalex]

But then, phase for sin(wt + 180) is (wt)??? Yes, the equivalent function is ?sin(wt). They both have the same phase, wt

How can the phase suddenly change from (wt + 179) to (wt) ??? Who said it was sudden?

Using the identity I gave you:

sin(u ? v) = sin (u)cos (v) ? cos(u)sin(v)
​

​

substituting u = wt and v = 179

The equivalent would be:

sin (wt + 179) = sin(wt)(cos(179) + cos(wt)sin(179)

= sin (wt) x -0.99985 + cos (wt)x0.01745)
​

= -0.99985 sin(wt) + 0.01745 cos(wt)
​

It?s a bit harder to work with in that form

Fortunately , sin(wt +180) works out much more easily:

Sin(wt + 180) = sin (wt)cos(180) + cos(wt)sin(180)

= sin (wt)x -1 + cos(wt)x0
​

=-sin (wt) +0
=-sin(wt)

​

That is, how can you make the phase constant go to zero in an instant??? It doesn't, its pretty much incremental. See above

I guess it is just over my thick head. Sounds like a discontinuity to me!

You ain't stupid - just thick. Apply the math skills, I actually know you have to make proper substitutions.

 

[rbalex]

...
The two waveforms can be expressed with reference to a common phase.
That they can doesn't make them the same phase.
....

Of course it is. In fact, the phase is identical for each function. ONE phase, a SINGLE phase, is all that is needed to express all relevant voltage functions for a conventional 120/240V system.

Oops ,I hit save too soon

....
They have a mutual phase displacement of 180deg.

Not if they start and finish at the same time.

Edit Add: What they actually have is a mutual amplitude displacement of 180deg

 

[handy10]

In any kind of consistent treatment of phase, one must take the absolute value of the amplitude and adjust the trig function accordingly. This is not a new doctrine. To say that Asin(t) and -Asin(t) have the same phase is incorrect.

Edit Add: What they actually have is a mutual amplitude displacement of 180deg

 

[rattus]

I am confused:

I am confused:

You ain't stupid - just thick. Apply the math skills, I actually know you have to make proper substitutions.

So the phase constant is not constant? Now how can that be? It is a constant is it not??

BTW, I have never seen trig identities used in that manner. I doubt that anyone else has either. Doesn't make sense that one can change the phase constant by any method. Surely you are putting us on.

Maybe you can provide a reference which validates this method??

I am so confused!

 

[Rick Christopherson]

BTW, I have never seen trig identities used in that manner. I doubt that anyone else has either. Doesn't make sense that one can change the phase constant by any method. Surely you are putting us on.

Maybe you can provide a reference which validates this method??

I am so confused!

It's a standard trig identity, Rattus. It is the one that allowed you to put the phase angle in in the first place. If this is news to you, it is simply because you forgot it, not because it wasn't taught to you. Whether you realized it or not, you have been using this identity through out this discussion, and it is the reason why I keep harping on the differences between an inversion and a phase shift.

 

[rbalex]

So the phase constant is not constant? Now how can that be? It is a constant is it not??

BTW, I have never seen trig identities used in that manner. I doubt that anyone else has either. Doesn't make sense that one can change the phase constant by any method. Surely you are putting us on.

Maybe you can provide a reference which validates this method??

I am so confused!

Vm sin ([ωt+φ₀]+180?) and -Vm sin ([ωt+φ₀]) are simply equivalent expressions and can validly replace each other. That's what identities do.

In those expressions u = ([ωt+φ₀]) and v = 180? when plugged into the left hand side of the general identity. (Try it, you'll like it) and, in this most general case, φ₀ doesn't disappear. Remember the phase constant just establishes what the expressions value is when t = 0. (Try it, you'll like it too - using any φ₀ you care to )

We went through this in MY college class when the Prof was dispelling the Myth to some former military techs. He never used an oscilloscope or other instrument - just the underlying math. He did it much faster.

 

[rattus]

It's a standard trig identity, Rattus. It is the one that allowed you to put the phase angle in in the first place. If this is news to you, it is simply because you forgot it, not because it wasn't taught to you. Whether you realized it or not, you have been using this identity through out this discussion, and it is the reason why I keep harping on the differences between an inversion and a phase shift.

I am not questioning the identity. I am questioning the conclusions reached by rbalex where he claims (wt + 180) = (wt). He has made the phase constant disappear. I am asking for a reference to support this position.

 

[Rick Christopherson]

I am not questioning the identity. I am questioning the conclusions reached by rbalex where he claims (wt + 180) = (wt). He has made the phase constant disappear. I am asking for a reference to support this position.

You made the phase constant appear in the first place. You're arguing against yourself. So this whole portion of the discussion makes no sense.

 

[rbalex]

...I am questioning the conclusions reached by rbalex where he claims (wt + 180) = (wt). ...

Be careful rattus that IS a false assertion.

 

[mivey]

Yes, move the test leads from a device that does not support your premise to one that does. That has been the arguement, moving the leads has been creating the effect you have been claiming.

You claimed the winding directions give the indication of the "correct" direction for leads. My generator example shows that the winding directions are not an indicator. The windings from the two 180? sources are aligned exactly the same as the center-tap windings. And don't point to the currents either because the currents travel exactly the same in both cases.

The phase reversal is there because you have reversed the leads relative to the winding's turn direction. If you maintain consistency of lead connection arrangement with winding turn direction, the phase reversal magically disappears.

No, one generator was simply rotated 180? relative to the other. No leads were changed.

This is where we agree. There is no need to claim the phases are reversed when it is the measuring method that has reversed. In fact, the transformer windings are in series, in phase, and this fact is fixed and determined at the time of manufacturing. This series, in phase, arrangement does not change, although the connections to the taps provided may change.

Nothing reversed. When you measure the 120/208 volt system are you "reversing" your measurements?

I do not understand why I must subtract the voltage vector supplied by you when I physically add windings in series and the real voltage actually adds. Can you explain this ?

If you want to stick with series addition, then look at my open-wye example. One series voltage is X1->X2+X3->X4 and the other is X2->X1+X6->X5. Both X1->X2 and X2->X1 directions are producing series voltage additions that result in a phase displacement.

X1->X2+X3->X4 gives you 120@0? + 120@0? = 240@0?

X2->X1+X6->X5 gives you 120@180? + 120@60? = 120@120?

These two series combinations have a physical phase difference and result from two different directions through the same winding.

Day to day EC's have been making this inquiry repeatedly, is there one phase or more than one. And your response, do you want to say that the need to understand this is "above and beyond".

I am both a EE and EC and I know that the difference will make no impact on day-to-day operations. If you have reason to think otherwise, let's hear it.

Here is a reality check for you: The last time the average person saw a phase shift, they were watching Star Trek or Stargate where stepping through the door that causes the phase shift would land them in an alternate parallel dimension, usually a punisment or hell dimension. The random phase shift is something to be afraid of. Considering that this is how the majority of the audience is trained, do you really want them to just blindly and obediently accept there is a phase shift at the transformer without conveying the fact that the phase shift is caused by how the load is connected to the transformer and not by the transformer itself. It is smoke and mirrors.

The average person probably could care less. The non-average person may have used something like a balun before and realized that the transformer does cause a 180? phase difference.

rattus maintains there is a phase shift and placed the leads where he could show his predetermined conclusion. However, the voltages he displays sum to zero while the actual voltages sum to 240. Yes, I know, I should subtract when I am adding. Can I have your pager number to call you when it's time to subtract when I am adding?

If you think you really need it and want to pay my fee, then you are sure welcome to call.

 

[rattus]

Vm sin ([ωt+φ₀]+180?) and -Vm sin ([ωt+φ₀]) are simply equivalent expressions and can validly replace each other. That's what identities do.

In those expressions u = ([ωt+φ₀]) and v = 180? when plugged into the left hand side of the general identity. (Try it, you'll like it) and, in this most general case, φ₀ doesn't disappear. Remember the phase constant just establishes what the expressions value is when t = 0. (Try it, you'll like it too - using any φ₀ you care to )

We went through this in MY college class when the Prof was dispelling the Myth to some former military techs. He never used an oscilloscope or other instrument - just the underlying math. He did it much faster.

I learned that identity in my Freshman year. I am questioning your conclusion. I would like to see a reference which says the phase constant can be changed through some trigonometry.

 

[rbalex]

I learned that identity in my Freshman year. I am questioning your conclusion. I would like to see a reference which says the phase constant can be changed through some trigonometry.

If you accept the identity; you accept the conclusion or you didn't learn what you were taught. Google "trigomometric identities." I'm not going to do your research for you.

 

[rattus]

If you accept the identity; you accept the conclusion or you didn't learn what you were taught. Google "trigomometric identities." I'm not going to do your research for you.

Nonsense! I learned identities from a math teacher. He said nothing about electrical phase. That came later.

The conclusion should be that a sine wave shifted by PI radians is equivalent to a negative sine function. That is the point your prof was making.

In my AC circuits course, we always used the sine function with a phase angle. There was NO hint that we should do anything else. I know also that Dr. Heizer, RIP, would call this notion silly.

You admit that the phase of sin(wt + 179) is (wt + 179), but you claim that the phase of sin(wt + 180) is (wt). That simply does not compute.

Now refer me to a source that supports your claim. If you can't that will mean that you are wrong. Don't tell me to do it either. It is your credibility at stake.

 

[rbalex]

Nonsense! I learned identities from a math teacher. He said nothing about electrical phase. That came later.

The conclusion should be that a sine wave shifted by PI radians is equivalent to a negative sine function. That is the point your prof was making.

In my AC circuits course, we always used the sine function with a phase angle. There was NO hint that we should do anything else. I know also that Dr. Heizer, RIP, would call this notion silly.

You admit that the phase of sin(wt + 179) is (wt + 179), but you claim that the phase of sin(wt + 180) is (wt). That simply does not compute.

Now refer me to a source that supports your claim. If you can't that will mean that you are wrong. Don't tell me to do it either. It is your credibility at stake.

I'm sorry, but your lack of comprehension isn't a particularly compelling argument for me to worry about my credibility with someone who has the competence. I believe you have the capacity to understand, but not the desire.

 

[rattus]

Not professional

Not professional

I'm sorry, but your lack of comprehension isn't a particularly compelling argument for me to worry about my credibility with someone who has the competence. I believe you have the capacity to understand, but not the desire.

So you can't support your position with a solid reference? I didn't think so.

It is unprofessional to respond with condescending remarks.

That indicates that you know you are wrong.

At least four engineers, with decades of experience think you are wrong.

Problem is that some members may actually believe your claims.

It is simply ludicrous to claim that the phase constant is not really the phase constant but is something else.

You finally gave in on the polarity/in phase issue. Why should anyone believe anything else you say?

No reference, no credibility!

 

[pfalcon]

My my, what busy beavers. Have been out of town for a bit and really thought the thread was going to devolve into an insult stream, but I see it has survived with some real discussion alive. Good responses by gar, besoeker, and rattus to the usual suspects.

Welcome back.

Nothing we are discussing will change the day-to-day life of the EC since it is "above and beyond" the understanding needed for day-to-day work.

On which we've always agreed.

Here is a reality check for you: How does telling the average person that the measuring equipment they are using is lying to them give them confidence and avoid fear, uncertainty, and doubt? The fact is, the equipment is showing you what is actually there. A meter is device measuring the effects of adding a small load, not a device that just makes up something to throw at the display.

No one in this thread has ever told anyone that the measuring equipment is lying to them. That's inappropriate to claim. You discredit yourself. Particularly in light of the prior section of your quote. This has nothing to do with day-to-day.

As rattus said in one of the prior posts, he did not reverse any leads because he put them where he wanted them in the first place.

Sure he did. And sure he wanted them that way. Those are not mutually exclusive as you imply. And it would show the same phase except he forgets to invert the magnitude before comparison. At any given instance in time except T=0 or 180; the current is flowing in one direction across the entire secondary coil. He measures one voltage with the current and one voltage against the current. Which would be fine but only if he remembered to invert one of the two voltages before beginning his comparison. The voltage-current relationship must be held constant before comparison.

 

[rattus]

Sure he did. And sure he wanted them that way. Those are not mutually exclusive as you imply. And it would show the same phase except he forgets to invert the magnitude before comparison. At any given instance in time except T=0 or 180; the current is flowing in one direction across the entire secondary coil. He measures one voltage with the current and one voltage against the current. Which would be fine but only if he remembered to invert one of the two voltages before beginning his comparison. The voltage-current relationship must be held constant before comparison.

Why would I invert one of the waveforms? I want the waveforms on L1 and L2, not their inverses.

And, what does current have to do with anything?

BTW, it is wt = 0 and wt = 180. t is measured in seconds, not degrees. Cap T is standard notation for the period, a constant, not a function of time.